Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $209.78   10.568%   $231.9496   $231.95   $231.95   $231.90  
  Purchase #2 $163.31   13.132%   $184.7559   $184.76   $184.75   $184.80  
  Purchase #3 $98.58   5.677%   $104.1764   $104.18   $104.20   $104.20  
  Purchase #4 $11.43   6.323%   $12.1527   $12.15   $12.15   $12.20  
  Purchase #5 $182.56   11.500%   $203.5544   $203.55   $203.55   $203.60  
  Purchase #6 $109.46   8.129%   $118.358   $118.36   $118.35   $118.40  
  Purchase #7 $133.44   10.536%   $147.4992   $147.50   $147.50   $147.50  
  7 purchase totals = $908.56       $1,002.4462   $1,002.45   $1,002.45   $1,002.60